Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$129.78	9.404%	$141.9845	$141.98	$142.00	$142.00
Purchase #2	$233.46	11.855%	$261.1367	$261.14	$261.15	$261.10
Purchase #3	$101.94	3.266%	$105.2694	$105.27	$105.25	$105.30
Purchase #4	$123.55	9.177%	$134.8882	$134.89	$134.90	$134.90
Purchase #5	$42.70	12.599%	$48.0798	$48.08	$48.10	$48.10
Purchase #6	$126.69	7.358%	$136.0119	$136.01	$136.00	$136.00
Purchase #7	$135.87	4.871%	$142.4882	$142.49	$142.50	$142.50
7 purchase totals =	$893.99		$969.8587	$969.86	$969.90	$969.90